* {
    margin: 0;
    padding: 0;
    list-style: none;
}
.head {
    width: 250px;
}

.head dt {
    height: 34px;
    line-height: 34px;
    padding-left: 20px;
    font-size: 13px;
    font-weight: 700;
    background-color: rgb(255, 250, 232);
}

.head dd a{
    /* 高度为0时就溢出所有的内容，并且隐藏 */
    overflow: hidden;
    height: 0;
    transition: all .7s ease 0s;
    line-height: 34px;
    background-color: blue;
    font-size: 12px;
    padding-left: 30px;
}